1. Field of the Invention
The present invention relates generally to drilling systems and more particularly to a system of drilling boreholes having a measurement-while-drilling (“MWD”) tool wherein the MWD tool has formation sensors, directional sensors, a power source, and a telemetry device integrated in a single tool no longer than a standard drill collar.
2. Description of the Related Art
Those skilled in the art have long recognized the importance of obtaining various borehole measurements during the course of a drilling operation. Typically, these measurements include such data as the weight imposed on the drill bit, the torque applied to the drill string, the inclination and azimuthal direction of the borehole interval that is then being drilled, borehole pressures and temperatures, drilling mud conditions as well as formation parameters including, but not limited to, resistivity and natural gamma emission of the earth formations being penetrated. Heretofore most of these measurements were obtained either by temporarily positioning special measuring devices in the drill string or by periodically removing the drill string and employing suitable wireline logging tools.
In recent years, however, the drilling technology has advanced sufficiently that these measurements can now be readily obtained by so-called measurement-while-drilling or “MWD” tools that are tandemly coupled in the drill string and operated during the drilling operation. Several MWD tools presently in commercial operation typically include a thick-walled tubular body carrying various sensors and their associated measurement-encoding circuitry which is preferably positioned in the drill string just above the drill bit for measuring the conditions near the bottom of the borehole. These commercial tools generally employ a selectively-operable acoustic signaler which is cooperatively arranged in the tool body for successively transmitting encoded measurement signals through the drilling mud within the drill string to the surface where the signals are detected and recorded by suitable surface instrumentation.
The typical commercial MWD tool is arranged as a multi-sectional tool having various special-purpose cartridges that are respectively housed in separable thick-walled bodies and suitably arranged to be coupled together in various combinations for assembling an MWD tool capable of obtaining one or more selected measurements. The multiple sections require both mechanical and electrical connections, such as the prior art arrangement shown in FIG. 1. It is essential that the electrical connectors in the tool bodies be protected from damage. A common problem is that when any tool is assembled while hanging in the slips on a rotary table, the threads on these thick-walled bodies will be damaged from time to time even though every precaution is used in handling the bodies. If the damage to the threads is not severe, the tool body may be returned to service after the threads are redressed. If the damage is more serious, the tool body must be reconditioned either by cutting off the damaged threads and rethreading the damaged end portion or by replacing the entire threaded end portion. In any event, once the tool body has been reconditioned, its overall length will be changed; and, before that body can be reused, some modification must be made to the connector or to any cartridge that is to be subsequently placed in that body before other tool bodies can be utilized with the reconditioned body. Another problem stems from the making and breaking of electrical connections outside of a protected environment, such as on a rig floor. Moisture or other contaminants typically cause reduced reliability of such connections. It will be appreciated that electrical connections between multiple tool sections, at the rig site, are a major reliability issue with MWD service.
The methods and apparatus of the present invention overcome the foregoing disadvantages of the prior art by providing an integrated MWD system which provides the basic downhole sensors in a single collar section. In addition, all tool electrical connections are made up in a controlled environment.